1. Field of the Invention
The present invention relates to a safety device for use in safety, such as a safety network controller and a safety I/O terminal.
2. Description of the Related Art
With an increase of interest in workplace safety, various safety devices have been proposed in recent years (For example, see Japanese Patent Application Laid-Open No. 2004-297997). These devices correspond to a safety network controller or a safety I/O terminal and are used with a cutting machine, a severing machine, or a manufacturing robot having an arm. A safety standard will be explained with an example of a safety network controller. A safety network controller is configured to include a safety self-diagnosis function in addition to a logical calculation function and an input and output control function which are similar to those of a typical programmable controller (PLC) in order to maintain high reliability in its control. Such safety network controller is sometimes referred to as “safety controller” or “safety master controller.” The safety network controller includes a function for performing a compulsory safety control (fail safe control) not to pose a danger by own control when an abnormality is detected in the result of the self-diagnosis. Accordingly, it prevents operations of the manufacturing robot from posing a danger. In more detail, “safety” stated here includes normalized safety standards. For example, IEC61508 and EN standard are known. According to the IEC61508 (International Electrotechnical Commission related to functional safety of programmable electronic systems), a probability of dangerous trouble (a probability of failure per hour) is defined and SIL level (Safety Integrity Level) is classified in four levels based on the probability. The EN standard evaluates degree of risk and requires a process for risk reduction. In EN954-1, there are five safety categories. The safety network controller or the like according to the present invention is compliant with one of these safety standards. The safety I/O terminal also includes a self-diagnosis function and a fail safe function for controlling not to pose a danger by own control when an abnormality is detected in the result of the self-diagnosis. Accordingly, it is prevented that danger is caused by an operation of the safety network controller or an operation of the manufacturing robot. Here, the safety I/O terminal is sometimes referred to as “safety slave station,” “safety slave unit,” or “safety slave.”
Conventionally, a safety control system in which a safety network controller and a safety I/O terminal are connected via a network is known. The safety network controller includes a communication master function for communicating with the safety I/O terminal and it is sometimes referred to as a safety master.
The safety I/O terminal includes a network communication function for communicating with the communication master function of the safety network controller, that is, a communication slave function controlled based on a master. The safety I/O terminal has a connecting terminal to which at least one of an input device such as a switch for outputting an on-off signal and an output device as a destination of a control signal is connected. As examples of the input device, there are an emergency stop switch SW, a light curtain, a door switch, and a two-hand switch. As examples of the output device, there are a safety relay and a contactor. These input device and output device are also compliant with safety standards. The safety I/O terminal generates control data based on a signal input from a connected input device and transmits the generated control data to the safety network controller via a network.
As a safety network controller, building type safety network controller which is composed of combination of a plurality of units such as a CPU unit, power source unit, I/O unit, and communication master unit. Each unit is coupled to a common internal bus and the CPU unit which governs the control of entire safety network controller communicates with other units via the bus to transmit and receive data. The coupled I/O unit also includes a connecting terminal to which an input device or an output device for use in safety is connected. The safety network controller inputs an input signal which is input from the safety I/O terminal via the communication master unit by network communication or an input signal of the input device connected to the coupled I/O unit and performs logical calculation for on/off of the input signal in use of a communication program. The safety network terminal outputs an output signal based on the calculation result to the safety I/O terminal via the communication master unit by network communication or the coupled I/O unit. The I/O unit and the safety I/O terminal output the output signal to the output device. By repeating this series of operation, the entire system including the manufacturing robot is controlled by the safety network controller. The communication cycle between the safety network controller and the safety I/O terminal may or may not be in synchronization with the cycle of the repetitive operation of the safety network controller.
The safety relay or the contactor as the output device connected to the safety I/O terminal is connected to the manufacturing robot, processing machine, severing machine or the like. The manufacturing robot or the like operates when the contact point with the relay or the contactor is on and the manufacturing robot or the like stops operating when the contact point is off. Accordingly, the safety network controller carries out control regarding operation stop of the operating robot or the like to be controlled by controlling on-off of the output device. Specifically, when a proper operation of an emergency stop switch SW is input from the safety I/O terminal via a network, the safety network controller turns off the output device (relay or contactor) to prevent the controlled subject from operating dangerously or promptly carries out a compulsory control in a safe condition and a necessary safety process. When a diagnosis result including abnormality of the emergency stop switch SW or other input devices is input, the safety network controller turns off the output device in order to stop the operation and prevent the controlled subject from operating dangerously or promptly carries out a compulsory control in a safe condition and a necessary safety process regardless of whether or not the emergency stop switch SW is operated or the input device is on. The I/O unit coupled with the safety network controller or the safety I/O terminal includes an input unit having one or more input terminals, an output unit having one or more output terminals, an/or a testing unit having one or more test terminals.
Here, “and/or” is used since a safety device for inputting generally does not include an output unit and a safety device for outputting generally dose not include an input unit. Further, in general, almost all safety devices include a testing unit.
Resent safety devices (for example, a safety network controller and a safety I/O terminal) are more downsized in relation to mounting spaces so that the number of terminals included in the input unit, the output unit, and the testing unit are restricted. As a result, it is more difficult to obtain a combination of the most preferable terminal specification in accordance with a relevant system while maintaining enough number of terminals. Especially, the number of test terminals and test terminal specifications, which constitute the testing unit, has been a more serious problem for product optimization due to diversification of input devices and output devices. In other words, in the I/O unit or the safety I/O terminal, the maximum number of terminals to be provided is limited in relation to space of housing surface although it is preferable that many input devices or output devices can be connected to a single I/O unit of safety I/O terminal. Accordingly, there has been a problem that the number of input terminals or output terminals reduces as the number of test terminals increases.
The present invention has been made in view of such technical background and has an object of providing a safety device that is flexibly adaptable to input devices and output devices having various functions and terminal structures with a single safety device.
Other objects and effects of the present invention should be easily appreciated by a person skilled in the art with reference to the following description.